The purpose of this proposal is to identify and characterize bacterial surface groups that react in a selective way with the Fc-regions of a variety of different immunoglobulin classes and subclasses from various mammals. The aim is to obtain molecules with reactivities differing from those of staphylococcal protein A which can then be used alone of in combination with protein A for a wide variety of selective immunoassays and in the purification of specific immunoglobulin classes and subclasses. The role of bacterial Fc-reactive proteins in the disease course and post-infection sequelae of certain infections will be explored as suitable reagents become available. In particular we propose to study the potential role of bacterial Fc-reactive proteins in the pathogenesis of post-streptococcal glomerulonephritis.